Friction Stir Spot Welding of Al-Cu with Different Zn Foils

In order to improve the quality of friction stir spot welding joint of Al-Cu dissimilar metals, the pure Zn foils with different thicknesses were selected as the interlayer to perform the experiments. The thickness of Zn foil affected the morphology of the lap interface and the thickness of the intermetallic compound layer. The structure and composition of IMCs layer of Zn-added joint were similar when the thickness of Zn foil varied from 0.02 to 0.1 mm. The IMCs layer at the lap interface of the Zn-added joint was composed of AlxCuyZnz, Al2Cu, and alpha Al + Al2Cu three sub-layers structure. The thickness of the IMCs layer increased with the increase in Zn thickness, and the joint obtained the smallest IMCs layer of 79 mu m with the addition of 0.02 mm Zn foil. The joint with 0.02 mm Zn foil obtained the maximum tensile shear load of 6.84 kN, which was 0.52 kN bigger than that of the joint without Zn foil. The fracture mode of the joints with 0.02 and 0.05 mm Zn foils was the quasi-cleavage characterized by cleavage surface, granular fracture surface and large tearing ridge, while the joint with 0.1 mm Zn and the joint without Zn foil belonged to the cleavage fracture.